Preamble structure and acquisition for a wireless communication system

ABSTRACT

Techniques for sending sector/system information in TDM pilots using a hierarchical pilot structure are described. A base station sends multiple sets of bits for the sector/system information in multiple TDM pilots. The set of bits sent in a given TDM pilot may include bits sent in earlier TDM pilots. In one design, the base station generates a first TDM pilot based on a first set of bits, generates a second TDM pilot based on a second set of bits that includes the first set, generates a third TDM pilot based on all bits for the information, and sends the TDM pilots. A terminal performs detection to obtain a first detected value for the first TDM pilot, performs detection based on the first detected value to obtain a second detected value for the second TDM pilot, and performs detection based on the first and second detected values to obtain a third detected value for the third TDM pilot.

The present application claims priority to provisional U.S. ApplicationSerial No. 60/813,483, entitled “HANDOFF SELECTION FOR WIRELESSCOMMUNICATION SYSTEMS,” filed Jun. 13, 2006, assigned to the assigneehereof and incorporated herein by reference.

BACKGROUND

I. Field

The present disclosure relates generally to communication, and morespecifically to acquisition techniques for a wireless communicationsystem.

II. Background

Wireless communication systems are widely deployed to provide variouscommunication services such as voice, video, packet data, messaging,broadcast, etc. These systems may be multiple-access systems capable ofsupporting communication for multiple users by sharing the availablesystem resources. Examples of such multiple-access systems include CodeDivision Multiple Access (CDMA) systems, Time Division Multiple Access(TDMA) systems, Frequency Division Multiple Access (FDMA) systems,Orthogonal FDMA (OFDMA) systems, and Single-Carrier FDMA (SC-FDMA)systems.

A wireless communication system may include many base stations thatsupport communication for many terminals. A terminal (e.g., a cellularphone) may be within the coverage of zero, one, or multiple basestations at any given moment. The terminal may have just been powered onor may have lost coverage and thus may not know which base stations canbe received. The terminal may perform acquisition to detect for basestations and to acquire timing and other information for the detectedbase stations. The terminal may use the acquired information to accessthe system via a detected base station.

Each base station may send transmissions to assist the terminals performacquisition. These transmissions represent overhead and should be sentas efficiently as possible. Furthermore, the transmissions should allowthe terminals to perform acquisition as quickly and robustly aspossible.

SUMMARY

Techniques for sending sector/system information in time divisionmultiplexed (TDM) pilots by a base station are described herein.Techniques for acquiring the sector/system information from the TDMpilots by a terminal are also described. In one aspect, thesector/system information is sent in the TDM pilots using a hierarchicalpilot structure. For the hierarchical pilot structure, multiple sets ofbits for the sector/system information may be sent in multiple TDMpilots, and the set of bits sent in a given TDM pilot may include bitssent in one or more earlier TDM pilots. The hierarchical pilot structuremay reduce acquisition complexity and improve detection performance forthe terminals while allowing a relatively large number of bits to besent for the sector/system information.

In one design of a 3-level hierarchical pilot structure, a base stationmay generate a first TDM pilot based on a first set of bits for thesector/system information. The base station may generate a second TDMpilot based on a second set of bits for the sector/system information,with the second set comprising the first set. The base station maygenerate a third TDM pilot based on all bits of the sector/systeminformation. The base station may send the first, second, and third TDMpilots in first, second, and third time intervals, respectively, in apreamble that is transmitted periodically.

A terminal may perform detection for the first TDM pilot to obtain afirst detected value for the first set of bits sent in the first TDMpilot. The terminal may perform detection for the second TDM pilot basedon the first detected value to obtain a second detected value for thesecond set of bits sent in the second TDM pilot. The terminal mayperform detection for the third TDM pilot based on the first and seconddetected values to obtain a third detected value for all bits of thesector/system information sent in the third TDM pilot.

A 2-level hierarchical pilot structure and a non-hierarchical pilotstructure are described below. Various aspects and features of thedisclosure are also described in further detail below.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a wireless communication system.

FIG. 2 shows a design of a superframe structure and a preamblestructure.

FIG. 3 shows a design of TDM pilots 1, 2 and 3 in the frequency domain.

FIG. 4A shows a design of a 3-level hierarchical pilot structure.

FIG. 4B shows a design of a 2-level hierarchical pilot structure.

FIG. 4C shows a design of a 3-level non-hierarchical pilot structure.

FIG. 5 shows a block diagram of a base station and a terminal.

FIG. 6 shows a block diagram of a transmit (TX) pilot processor and amodulator at the base station.

FIG. 7 shows a block diagram of an acquisition processor at theterminal.

FIG. 8 shows a process performed by the base station to send TDM pilots.

FIG. 9 shows an apparatus for sending TDM pilots.

FIG. 10 shows a process performed by the terminal to receive TDM pilots.

FIG. 11 shows an apparatus for receiving TDM pilots.

DETAILED DESCRIPTION

FIG. 1 shows a wireless communication system 100 with multiple basestations 110 and multiple terminals 120. A base station is a stationthat communicates with the terminals. A base station may also be called,and may contain some or all of the functionality of, an access point, aNode B, an evolved Node B, etc. Each base station 110 providescommunication coverage for a particular geographic area 102. The term“cell” can refer to a base station and/or its coverage area depending onthe context in which the term is used. To improve system capacity, abase station coverage area may be partitioned into multiple smallerareas, e.g., three smaller areas 104 a, 104 b, and 104 c. Each smallerarea may be served by a respective base transceiver station (BTS). Theterm “sector” can refer to a BTS and/or its coverage area depending onthe context in which the term is used. For a sectorized cell, the BTSsfor all sectors of that cell are typically co-located within the basestation for the cell. The techniques described herein may be used forsystems with sectorized cells as well as systems with unsectorizedcells. For clarity, the techniques are described below for a system withsectorized cells.

Terminals 120 are typically dispersed throughout the system, and eachterminal may be stationary or mobile. A terminal may also be called, andmay contain some or all of the functionality of, an access terminal, amobile station, a user equipment, a subscriber unit, a station, etc. Aterminal may be a cellular phone, a personal digital assistant (PDA), awireless device, a wireless modem, a handheld device, a laptop computer,etc. A terminal may communicate with zero, one, or multiple basestations on the forward and/or reverse link at any given moment. Theforward link (or downlink) refers to the communication link from thebase stations to the terminals, and the reverse link (or uplink) refersto the communication link from the terminals to the base stations.

For a centralized architecture, a system controller 130 couples to basestations 110 and provides coordination and control for these basestations. System controller 130 may be a single network entity or acollection of network entities. For a distributed architecture, basestations 110 may communicate with one another as needed.

The techniques described herein may be used for various wirelesscommunication systems such as CDMA, TDMA, FDMA, OFDMA and SC-FDMAsystems. A CDMA system utilizes code division multiplexing (CDM) andsends transmissions with different orthogonal codes. A TDMA systemutilizes time division multiplexing (TDM) and sends transmissions indifferent time slots. An FDMA system utilizes frequency divisionmultiplexing (FDM) and sends transmissions on different subcarriers. AnOFDMA utilizes orthogonal frequency division multiplexing (OFDM), and anSC-FDMA system utilizes single-carrier frequency division multiplexing(SC-FDM). OFDM and SC-FDM partition the system bandwidth into multipleorthogonal subcarriers, which are also referred to as tones, bins, etc.Each subcarrier may be modulated with data. In general, modulationsymbols are sent in the frequency domain with OFDM and in the timedomain with SC-FDM. The techniques may also be used for wirelesscommunication systems that utilize a combination of multiplexingschemes, e.g., CDMA and OFDM, or OFDM and SC-FDM, etc. For clarity,certain aspects of the techniques are described below for a system thatutilizes OFDM on the forward link.

System 100 may utilize a superframe structure for transmissions sent onthe forward link from the base stations to the terminals. The superframestructure may be defined in various manners and may include variousfields.

FIG. 2 shows a design of a superframe structure 200 that may be used forthe forward link. In this design, the transmission timeline ispartitioned into units of superframes. Each superframe spans aparticular time duration, which may be fixed or configurable. Eachsuperframe includes a preamble followed by Q frames, where in generalQ≧1 and in one design Q=24. The preamble carries pilots and overheadinformation that enable the terminals to acquire the transmitting basestation, receive forward link control channels, and subsequently accessthe system. Each frame may carry traffic data and/or signaling and mayspan a predetermined time duration.

FIG. 2 also shows a design of the preamble. In this design, the preamblespans eight OFDM symbols that are assigned indices of 1 through 8. Thefirst five OFDM symbols with indices of 1 through 5 are used for one ormore primary Broadcast Channels (pBCHs). The pBCHs may carry (i)information for deployment-specific parameters such as total number ofsubcarriers, number of guard subcarriers, system time, etc., and (ii)sector-specific parameters such as frequency hopping structure, pilotstructure, control channel structure, number of transmit antennas, etc.The last three OFDM symbols with indices of 6, 7 and 8 are used for TDMpilots 1, 2 and 3, respectively. The TDM pilots may carry sector/systeminformation and may be used for acquisition by terminals attempting toaccess the system. In the design shown in FIG. 2, the TDM pilots aresent periodically in the preamble of each superframe, and each TDM pilotis sent in one OFDM symbol period.

FIG. 2 shows a specific superframe structure and a specific preamblestructure for the forward link. In general, a superframe may span anytime duration and may include any number of frames and other fields. Apreamble may also span any time duration and include any number offields. A preamble may include any number of TDM pilots, e.g., two,three, four, or some other number of TDM pilots. Each TDM pilot may spanany number of OFDM symbol periods. For clarity, the followingdescription assumes that three TDM pilots are sent in the preamble.

TDM pilots 1, 2 and 3 may be designed to facilitate acquisition by theterminals. A terminal may use TDM pilot 1 to detect for the presence ofa preamble and to acquire coarse timing and frequency. The terminal mayuse TDM pilots 1, 2 and/or 3 to obtain sector/system information.

FIG. 3 shows a design of TDM pilots 1, 2 and 3 in the frequency domain.In this design, TDM pilot 1 is sent on every N₁ subcarriers, TDM pilot 2is sent on every N₂ subcarriers, and TDM pilot 3 is sent on every N₃subcarriers, where N₁, N₂ and N₃ may each be any integer one or greater.As an example, N_(p) may be equal to two for TDM pilot p, where p ε{1,2, 3}, and TDM pilot p may be sent on K/2 subcarriers with either evenor odd indices. Zero symbols with signal values of zero may be sent onsubcarriers not used for the TDM pilot. For a given TDM pilot, sendingpilot symbols on every N_(p) subcarriers in the frequency domain resultsin N_(p) copies of the same TDM pilot waveform in the time domain. Thiswaveform contains L_(p)=K/N_(p) samples and may be obtained byperforming an L_(p)-point fast Fourier transform (FFT) on L_(p) pilotsymbols sent on L_(p) subcarriers used for the TDM pilot.

In general, each TDM pilot may be sent on all K subcarriers with N_(p)=1or on a subset of the K subcarriers with N_(p)>1. The TDM pilots may besent with the same number of subcarriers or with different numbers ofsubcarriers. The TDM pilots may also be sent on the same subcarriers oron different subcarriers.

Sector/system information may be sent in the TDM pilots. In general, thesector/system information may comprise any type of information such assector-specific information, system information, etc. Thesector-specific information may include a sector identifier (ID)identifying the sector sending the TDM pilots, a preferred carrier indexindicating a carrier preferred by the sector and used to assist handofffor terminals, etc. The system information may include a mode flag thatindicates whether the system is operating in a synchronous mode or anasynchronous mode, the cyclic prefix length, system time, etc. Thesector/system information may be used to receive forward linktransmissions sent by the sector and for communication with the sector.The sector/system information may include M bits, where in general M maybe any integer value and in one design M=12.

In an aspect, the sector/system information is sent in the TDM pilotsusing a hierarchical pilot structure. For the hierarchical pilotstructure, multiple sets of bits for the sector/system information maybe sent in multiple TDM pilots, and the set of bits sent in a given TDMpilot may include bits sent in one or more earlier TDM pilots. Thehierarchical pilot structure may reduce acquisition complexity andimprove detection performance for the terminals while allowing arelatively large number of bits to be sent for the sector/systeminformation. Several hierarchical pilot designs are described below.

FIG. 4A shows a design of a 3-level hierarchical pilot structure 400. Inthis design, the M bits of the sector/system information are partitionedinto M₁ least significant bits (LSBs), M₂ more significant bits, and M₃most significant bits (MSBs), where M=M₁+M₂+M₃. In general, M, M₁, M₂and M₃ may each be any integer value. In one design, M=12, M₁=2, M₂=6,and M₃=4. Other values may also be used for M, M₁, M₂ and M₃.

The M₁ LSBs of the sector/system information may be sent in TDM pilot 1.For example, the M₁ LSBs may be used as a seed value for a pseudo-randomnumber (PN) generator, and a PN sequence from the PN generator may beused to generate pilot symbols for TDM pilot 1. The M₁+M₂ LSBs of thesector/system information may be sent in TDM pilot 2, e.g., by seedingthe PN generator with the M₁+M₂ LSBs and using the resultant PN sequenceto generate pilot symbols for TDM pilot 2. All M bits of thesector/system information may be sent in TDM pilot 3, e.g., by seedingthe PN generator with all M bits and using the resultant PN sequence togenerate pilot symbols for TDM pilot 3. TDM pilots 1, 2 and 3 may thusbe “scrambled” by different PN sequences generated with differentportions of the sector/system information, where each portion mayinclude some or all of the sector/system information.

TDM pilot 1 may be sent on every N, subcarriers, as shown in FIG. 3. Inthis case, N₁ copies of the same waveform may be sent for TDM pilot 1. Acyclic prefix (CP) may be appended prior to the first waveform copy. TDMpilot 2 may be sent on every N₂ subcarriers. In this case, N₂ copies ofthe same waveform may be sent for TDM pilot 2. TDM pilot 3 may be senton every N₃ subcarriers. In this case, N₃ copies of the same waveformmay be sent for TDM pilot 3. Each waveform may be a specific sequence ofcomplex-valued samples.

In one design with M=12, TDM pilot 1 may be scrambled with M₁=2 bits ofinformation and may take on four possible values, TDM pilot 2 may bescrambled with M₁+M₂=8 bits of information and may take on 256 possiblevalues, and TDM pilot 3 may be scrambled with M=12 bits of informationand may take on 4096 possible values. A terminal may process TDM pilot 1and detect for one of four possible values for TDM pilot 1. The terminalmay then process TDM pilot 2 and detect for one of 64 possible valuesassociated with the detected value V₁ for TDM pilot 1. The terminal maythen process TDM pilot 3 and detect for one of 16 possible valuesassociated with the detected values V₁ and V₂ for TDM pilots 1 and 2,respectively. By performing acquisition in three stages, the terminalcan detect for one of 4096 possible values for the 12-bit sector/systeminformation by checking only 84 hypotheses, which include 4 hypothesesfor TDM pilot 1, 64 hypotheses for TDM pilot 2, and 16 hypotheses forTDM pilot 3. Acquisition complexity may be greatly reduced with thehierarchical pilot structure.

FIG. 4B shows a design of a 2-level hierarchical pilot structure 410. Inthis design, the M bits of the sector/system information are partitionedinto M_(a) MSBs and M_(b) LSBs, where M=M_(a)+M_(b). In general, M,M_(a) and M_(b) may each be any integer value. TDM pilot 1 may be sentwithout any sector/system information and may be common for all sectorsin the system. The M_(a) MSBs of the sector/system information may besent in TDM pilot 2, e.g., by seeding the PN generator with the M_(a)MSBs and using the resultant PN sequence to generate pilot symbols forTDM pilot 2. All M bits of the sector/system information may be sent inTDM pilot 3, e.g., by seeding the PN generator with all M bits and usingthe resultant PN sequence to generate pilot symbols for TDM pilot 3.

A terminal may process TDM pilot 1 for preamble detection and coarsetiming and frequency acquisition. The terminal may then process TDMpilot 2 and detect for one of 2^(M) ^(a) possible values for TDM pilot2. The terminal may then process TDM pilot 3 and detect for one of 2^(M)^(b) possible values associated with the detected value V_(a) for TDMpilot 2. By performing acquisition in two stages, the terminal candetect for one of 2^(M) ^(a) ^(+M) ^(b) possible values for thesector/system information by checking only 2^(M) ^(a) +2^(M) ^(b)hypotheses.

In the hierarchical pilot designs shown in FIGS. 4A and 4B, each TDMpilot that is embedded with sector/system information carries (i) allinformation bits sent in prior TDM pilots, if any, and (ii) additionalinformation bits not sent in prior TDM pilots. In another design, M₁bits are sent in TDM pilot 1, M₂ bits are sent in TDM pilot 2, and all Mbits are sent in TDM pilot 3. In yet another design, M₁ bits are sent inTDM pilot 1, M₁ and M₂ bits are sent in TDM pilot 2, and M₂ and M₃ bitsare sent in TDM pilot 3. Various other hierarchical pilot designs arealso possible. In general, for a hierarchical pilot, at least one bit ofthe sector/system information is sent in multiple TDM pilots, and atleast one TDM pilot carries at least one bit sent in a prior TDM pilot.

A hierarchical pilot may improve detection performance by reducing thelikelihood of false alarm. For example, in the design shown in FIG. 4A,an interfering sector may have the same M₂ bits as a desired sector, butmay have different M₁ bits. In this case, the interfering sector may beeliminated because the M₁ and M₂ bits are sent in TDM pilot 2, and onlythe desired sector matches both M₁ and M₂ bits whereas the interferingsector matches the M₂ bits but does not match the M₁ bits.

The sector/system information may also be sent in a non-hierarchicalpilot structure. For a non-hierarchical pilot structure, each bit of thesector/system information is sent in only one TDM pilot. The TDM pilotsthus carry non-overlapping sets of bits for the sector/systeminformation.

FIG. 4C shows a design of a 3-level non-hierarchical pilot structure420. In this design, the M₁LSBs of the sector/system information may besent in TDM pilot 1. The M₂ more significant bits of the sector/systeminformation may be sent in TDM pilot 2. The M₃ MSBs of the sector/systeminformation may be sent in TDM pilot 3.

FIGS. 4A, 4B and 4C show some example designs of hierarchical andnon-hierarchical pilot structures. Various other pilot structures mayalso be defined. In general, a pilot structure may include any number oflevels, and any set of bits for the sector/system information may besent in each TDM pilot.

In the designs described above, some or all of the bits of thesector/system information may be used to generate a PN sequence, whichmay then be used to generate pilot symbols for a TDM pilot. Thesector/system information may also be sent in the TDM pilots in othermanners. In general, it may be desirable to send the sector/systeminformation in a manner such that the TDM pilots for each sector appearrandom to other sectors. This may randomize inter-sector interference,which may improve detection performance.

FIG. 5 shows a block diagram of a design of a base station 110 and aterminal 120, which may be one of the base stations and terminals inFIG. 1. For simplicity, only processing units for transmissions on theforward link are shown in FIG. 5. Also for simplicity, base station 110and terminal 120 are each equipped with a single antenna.

At base station 110, a TX pilot processor 510 generates pilot symbolsfor TDM pilots based on the sector/system information. As used herein, apilot symbol is a symbol for pilot, a data symbol is a symbol for data,a zero symbol is a symbol with a signal value of zero, and a symbol istypically a complex value. The data and pilot symbols may be modulationsymbols from modulation schemes such as PSK, QAM, etc. Pilot istypically data that is known a priori by both a transmitter and areceiver. However, the pilot symbols may be embedded with sector/systeminformation that is not known a priori by a receiver. A TX dataprocessor 520 receives traffic data and signaling data, processes thereceived data, and provides data symbols. A modulator (MOD) 522 performsmodulation on the data and pilot symbols (e.g., for OFDM) and providesoutput samples. A transmitter (TMTR) 524 processes (e.g., converts toanalog, amplifies, filters, and upconverts) the output samples andgenerates a forward link signal, which is transmitted via an antenna526.

At terminal 120, an antenna 552 receives the forward link signal frombase station 110 and provides a received signal to a receiver (RCVR)554. Receiver 554 processes (e.g., filters, amplifies, downconverts, anddigitizes) the received signal and provides received samples. Anacquisition processor 560 performs acquisition based on the TDM pilotsand provides timing, frequency, and sector/system information. Ademodulator (DEMOD) 570 performs demodulation on the received samples(e.g., for OFDM) to obtain data symbol estimates. A receive (RX) dataprocessor 572 processes the data symbol estimates in a mannercomplementary to the processing by TX data processor 520 and providesdecoded data.

Controllers 530 and 580 direct the operation at base station 110 andterminal 120, respectively. Memories 532 and 582 store program codes anddata for base station 110 and terminal 120, respectively.

FIG. 6 shows a block diagram of a design of TX pilot processor 510 andmodulator 522 at base station 110 in FIG. 5. Within processor 510, aunit 612 receives the sector/system information for a sector and a TDMpilot index that indicates whether TDM pilot 1, 2 or 3 is being sent. Inone design, unit 612 provides the sector/system information directly. Inthis design, the TDM pilots are static and do not change from superframeto superframe. In another design, unit 612 varies the sector/systeminformation based on system time, e.g., a superframe index. In thisdesign, the TDM pilots change from superframe to superframe, which mayrandomize the interference due to the TDM pilots. For this design, aterminal in a given sector y may observe randomized interference due tothe TDM pilots from other sectors. This may allow the terminal toperform correlation for the TDM pilots from sector y across more thanone superframe in order to detect for a weak preamble from sector y.

In any case, unit 612 provides M_(p) bits of the sector/systeminformation for TDM pilot p, where p ε{1, 2, 3} and 0≦M_(p)≦M. In thedesign shown in FIG. 4A, unit 612 provides M₁ LSBs of the sector/systeminformation for TDM pilot 1, M₁+M₂ LSBs of the sector/system informationfor TDM pilot 2, and all M bits of the sector/system information for TDMpilot 3. For the design shown in FIG. 4B, unit 612 provides zero bitsfor TDM pilot 1, M_(a) MSBs of the sector/system information for TDMpilot 2, and all M bits of the sector/system information for TDM pilot3. Unit 612 may provide other sets of information bits for the TDMpilots in other designs.

A PN generator 614 generates a PN sequence for TDM pilot p based on theM_(p) information bits received from unit 612. A scrambler 616 generatespilot symbols for TDM pilot p based on the PN sequence received from PNgenerator 614. Scrambler 616 may form groups of B bits based on the bitsin the PN sequence, map each group of B bits to a modulation symbol in amodulation scheme, and provide the modulation symbols for the groups ofB bits as the pilot symbols for TDM pilot p. B may be equal to 1 forBPSK, 2 for QPSK, etc. Scrambler 616 may also scramble known modulationsymbols with the PN sequence to generate the pilot symbols. Asymbol-to-subcarrier mapper 618 maps the pilot symbols for TDM pilot pto the subcarriers used for TDM pilot p, maps zero symbols to theremaining subcarriers, and provides K output symbols for the K totalsubcarriers to modulator 522.

Within modulator 522, a multiplexer (Mux) receives the output symbolsfrom TX pilot processor 510 and TX data processor 520, provides theoutput symbols from processor 510 during TDM pilot intervals, andprovides the output symbols from processor 520 during other intervals.In each OFDM symbol period, an FFT unit 624 performs a K-point FFT on Koutput symbols for the K total subcarriers to obtain K time-domainsamples. The K samples may include multiple copies of a waveform if thepilot symbols are mapped to uniformly spaced subcarriers, e.g., as shownin FIGS. 3, 4A, 4B and 4C. A unit 626 appends a cyclic prefix to the Ksamples by copying the last C samples and appending these C copiedsamples to the front of the K samples, where C is the cyclic prefixlength.

Terminal 120 may perform acquisition based on the TDM pilots in variousmanners. The received samples from receiver 554 may be expressed as:

r _(i) =x _(i) +n _(i),   Eq (1)

where x_(i) is a sample sent by base station 110 in sample period i,

-   -   r_(i) is a sample received by terminal 120 in sample period i,        and    -   n_(i) is the noise in sample period i.

Multiple copies of the same waveform may be sent for TDM pilot 1, e.g.,as shown in FIGS. 4A and 4B. In this case, terminal 110 may performdelayed correlation to detect for TDM pilot 1, as follows:

$\begin{matrix}{{C_{i} = {{\sum\limits_{j = 0}^{L_{1} - 1}{r_{i - j - L_{1}} \cdot r_{i - j}^{*}}}}^{2}},} & {{Eq}\mspace{14mu} (2)}\end{matrix}$

where C_(i) is a delayed correlation result for sample period i,

-   -   L₁ is the length of the waveform for TDM pilot 1, and    -   “*” denotes a complex conjugate.

The delayed correlation in equation (2) removes the effect of thewireless channel without requiring a channel estimate and furthercoherently combines the received energy across the length of thewaveform for TDM pilot 1. A sliding delayed correlation may be performedto obtain a delayed correlation result C_(i) for each sample period i.C_(i) may be compared against a threshold C_(th) to detect for TDM pilot1. For example, TDM pilot 1 may be declared if C_(i) exceeds C_(th) andremains above C_(th) for a predetermined percentage of L₁. The sampleperiod that results in the largest value of C_(i) may be provided as thecoarse timing, which is an indication of TDM pilot 1 position.

A coarse frequency error estimate Δf may be derived as follows:

$\begin{matrix}{{{\Delta \; f} = {\frac{1}{2{\pi \cdot L_{1} \cdot T_{sample}}} \cdot {\arctan \lbrack {\sum\limits_{j = 0}^{L_{1} - 1}{r_{i - j - L_{1}} \cdot r_{i - j}^{*}}} \rbrack}}},} & {{Eq}\mspace{14mu} (3)}\end{matrix}$

where T_(sample) is one sample period. The quantity r_(1−j−L) ₁·r_(i-j)* gives the phase shift from sample r_(i−j−L) ₁ to sampler_(1−j), which is L₁ sample periods later. The summation in equation (3)gives the average phase shift across L₁ sample periods. The division by2π·L₁·T_(sample) provides a per-sample frequency error estimate, inunits of radians.

The frequency error estimate Δf may be used to adjust the frequency of alocal oscillator (LO) signal used for frequency downconversion byreceiver 554. The received samples from receiver 554 may also be rotatedby Δf to remove the frequency error. The frequency error may also beremoved in other manners.

After acquiring coarse timing, the first TDM pilot carryingsector/system information may be captured to obtain at least one copy ofthe waveform for that TDM pilot. This first TDM pilot is TDM pilot 1 forthe design shown in FIG. 4A and is TDM pilot 2 for the design shown inFIG. 4B. The TDM pilot being detected is referred to as TDM pilot p inthe description below, where p ε{1, 2, 3}. TDM pilot p contains N_(p)copies of the same waveform, and the waveform contains L_(p) samples. Upto N_(p) copies of the waveform may be captured and processed to detectfor the information bits sent in TDM pilot p. For example, if TDM pilotp contains two copies of the waveform, then TDM pilot p may be sampledapproximately ¼ OFDM symbol period from the detected OFDM symbolboundary and for ½ OFDM symbol period to obtain K/2 captured samples forone complete copy of the waveform. For simplicity, the followingdescription assumes that one copy of the waveform for TDM pilot p iscaptured and processed.

A noise estimate σ² may be derived based on the L_(p) captured samplesfor TDM pilot p, as follows:

$\begin{matrix}{{\sigma^{2} = {\frac{1}{L_{p}} \cdot {\overset{L_{p}}{\sum\limits_{j}}{r_{j}}^{2}}}},} & {{Eq}\mspace{14mu} (4)}\end{matrix}$

where r_(j) is the j-th captured sample for TDM pilot p.

M_(p) bits of sector/system information may be sent in TDM pilot p. Todetermine the value of the M_(p) bits sent in TDM pilot p, a decisionmetric may be computed for each of the possible values that might havebeen sent in TDM pilot p. The value with the best decision metric may bedeclared as the value sent in TDM pilot p. The detection of thetransmitted value may be performed in various manners.

In one design, the L_(p) captured samples may be transformed to thefrequency domain with an FFT to obtain L_(p) received symbols. For eachhypothesis corresponding to a different value m hypothesized to havebeen sent in TDM pilot p, where 0≦m<2^(M) ^(p) for the first TDM pilotbeing detected, a PN sequence may be generated for hypothesized value m.The L_(p) received symbols may be descrambled with the PN sequence, andthe L_(p) descrambled symbols may be transformed back to the time domainwith an IFFT to obtain L_(p) descrambled samples. A detection metricE_(m) may be computed for hypothesized value m, as follows:

$\begin{matrix}{{{E_{m} = {\overset{L_{p}}{\sum\limits_{j}}{{{c_{j,m}}^{2} - {\eta \cdot \sigma^{2}}}}}},{or}}{{E_{m} = {\overset{L_{p}}{\sum\limits_{\{{j,{{c_{j,m}}^{2} > {\eta \cdot \sigma^{2}}}}\}}}{c_{j,m}}^{2}}},}} & {{Eq}\mspace{14mu} (5)}\end{matrix}$

where c_(j,m) is the j-th descrambled sample for hypothesized value m,and

-   -   η is a predetermined factor.

A detection metric may be computed for each of the 2^(M) ^(p) possiblevalues that might have been sent in TDM pilot p. The 2^(M) ^(p)detection metrics may be denoted as E_(m), for m=0, 1, . . . , 2^(M)^(p) −1. The hypothesized value with the largest detection metric may bedeclared as a detected value V_(p), which is the value deemed to havebeen sent for the M_(p) bits carried in TDM pilot p.

The detection described above may be repeated for each subsequent TDMpilot carrying some or all of the sector/system information. For eachTDM pilot, the detected values from all previously detected TDM pilotsmay be used to form all possible values for the bits sent in that TDMpilot.

For the design shown in FIG. 4A, the detected value V₁ for the M₁information bits sent in TDM pilot 1 may be used to form 2^(M) ²possible (M₁+M₂)-bit values that might have been sent in TDM pilot 2.Each possible value for TDM pilot 2 is composed of the detected value V₁for TDM pilot 1 and a hypothesized value m for the M₂ new bits sent inTDM pilot 2, where 0≦m<2^(M) ² . Similarly, the detected value V₁ forthe M₁ information bits sent in TDM pilot 1 and the detected value V₂for the M₂ information bits sent in TDM pilot 2 may be used to form2^(M) ³ possible M-bit values that might have been sent in TDM pilot 3.Each possible value for TDM pilot 3 is composed of the detected value V₁for TDM pilot 1, the detected value V₂ for TDM pilot 2, and ahypothesized value m for the M₃ new bits sent in TDM pilot 3, where0≦m<2^(M) ³ .

For the design shown in FIG. 4B, the detected value V_(a) for the M_(a)information bits sent in TDM pilot 2 may be used to form 2^(M) ^(b)possible M-bit values that might have been sent in TDM pilot 3. Eachpossible value for TDM pilot 3 is composed of the detected value V_(a)for TDM pilot 2 and a hypothesized value m for the M_(b) new bits sentin TDM pilot 3, where 0≦m<2^(M) ^(b) .

For each TDM pilot p, detection metrics may be computed for all possiblevalues for TDM pilot p, e.g., as shown in equations (4) and (5). Thehypothesized value with the largest detection metric may be declared asthe detected value for TDM pilot p.

FIG. 7 shows a block diagram of a design of acquisition processor 560 atterminal 120 in FIG. 5. Within processor 560, a delayed correlator 712obtains the received samples from receiver 554 and performs slidingdelayed correlation, e.g., as shown in equation (2). A TDM pilotdetector 714 receives the correlation results C_(i) from delayedcorrelator 712 and detects for TDM pilot 1. After detecting TDM pilot 1,detector 714 determines coarse timing and frequency error estimate Δfbased on the received samples that result in the detection of TDM pilot1.

A rotator 722 rotates the received samples based on the frequency errorestimate Δf and provides rotated samples having the frequency errorremoved. For each TDM pilot carrying sector/system information, a unit724 may capture samples for one or more copies of the waveform for thatTDM pilot, based on the coarse timing from detector 714. A unit 726derives a noise estimate for the captured samples, e.g., as shown inequation (4). An FFT unit 728 performs an FFT on the captured samplesand provides received symbols. A PN generator 730 generates a PNsequence for each possible value that might have been sent in the TDMpilot being detected. The PN sequences for the TDM pilot currently beingdetected may be dependent on the detected values for previously detectedTDM pilots, if any. For each hypothesized value m, a descrambler 732descrambles the received symbols with the corresponding PN sequence andprovides descrambled symbols. Descrambler 732 essentially removes themodulation on the received symbols with the PN sequence. The descrambledsymbols contain mostly noise if the locally generated PN sequence is notthe PN sequence sent in the TDM pilot being detected. An IFFT unit 734performs an IFFT on the descrambled symbols and provides descrambledsamples c_(j,m).

A unit 736 computes the detection metric E_(m) for each hypothesizedvalue m based on the descrambled samples and the noise estimate, e.g.,as shown in equation (5). A detector 738 receives the detection metricsE_(m) for all possible values that might have been sent in the TDM pilotbeing detected. Detector 738 identified the hypothesized value with thelargest detection metric and provides this value as the detected valueV_(p) for the TDM pilot being detected. PN generator 730 may receive thedetected value V_(p) from detector 738 and use this value to generate PNsequences for the next TDM pilot to be detected. After all TDM pilotsare detected, detector 738 provides the final detected value as therecovered sector/system information.

FIG. 7 shows one design for performing detection for the TDM pilots. Inanother design, the captured samples for a given TDM pilot arecorrelated with each possible waveform that might have been sent forthat TDM pilot. Different possible waveforms may be generated based ondifferent hypothesized values for the TDM pilot. The hypothesized valuewith the largest correlation result may be provided as the detectedvalue for the TDM pilot. The detection for the TDM pilots may also beperformed in other manners.

After detecting all TDM pilots, one or more TDM pilots may be used toderive fine timing and/or a fine frequency error estimate. OFDM symbolsmay be received and processed based on the fine timing and/or finefrequency error estimate.

FIG. 8 shows a design of a process 800 performed by a base station tosend TDM pilots. A plurality of pilots may be generated based ondifferent sets of bits for information being sent in the plurality ofpilots, with each set including some or all bits of the informationbeing sent (block 812). The information being sent may comprisesector-specific information, system information, etc. The plurality ofpilots may be sent in sequential order in a plurality of time intervals(block 814).

For a hierarchical pilot structure, the plurality of pilots may carryoverlapping sets of bits, e.g., as shown in FIGS. 4A and 4B. The set ofbits sent in each pilot may comprise bits sent in pilots transmittedearlier, if any, and additional bits not yet sent. For a 2-levelhierarchical pilot structure, a first pilot may be generated based onsome of the bits for the information, and a second pilot may begenerated based on all of the bits for the information. For a 3-levelhierarchical pilot structure, a first pilot may be generated based on afirst set of bits, a second pilot may be generated based on a second setof bits, which may comprise the first set, and a third pilot may begenerated based on all of the bits for the information. For anon-hierarchical pilot structure, the plurality of pilots may carrynon-overlapping sets of bits for the information, e.g., as shown in FIG.4C.

For each pilot, a PN sequence may be generated based on the set of bitsbeing sent in the pilot. Pilot symbols may be generated based on the PNsequence and mapped to subcarriers used for the pilot. The mapped pilotsymbols may be transformed to obtain a sequence of samples for thepilot. A given pilot may comprise one or multiple copies of a waveform.

FIG. 9 shows a design of an apparatus 900 for sending TDM pilots.Apparatus 900 includes means for generating a plurality of pilots basedon different sets of bits for information being sent in the plurality ofpilots, with each set including some or all bits of the informationbeing sent (module 912), and means for sending the plurality of pilotsin sequential order in a plurality of time intervals (module 914).

FIG. 10 shows a design of a process 1000 performed by a terminal toreceive TDM pilots. A plurality of pilots may be received in a pluralityof time intervals (block 1012). The plurality of pilots may carrydifferent sets of bits for information sent in the pilots, with each setincluding some or all bits of the information. Detection may beperformed to recover a set of bits sent in each of the plurality ofpilots (block 1014).

For a hierarchical pilot structure, detection for each pilot may beperformed based on detected values for pilots previously detected, ifany, to obtain a detected value for the set of bits sent in the pilotbeing detected. For a 2-level hierarchical pilot structure, detectionfor a first pilot may be performed to obtain a first detected value fora first set of bits sent in the first pilot. Detection for a secondpilot may be performed based on the first detected value to obtain asecond detected value for all bits of the information. For a 3-levelhierarchical pilot structure, detection for a first pilot may beperformed to obtain a first detected value for a first set of bits sentin the first pilot. Detection for a second pilot may be performed basedon the first detected value to obtain a second detected value for asecond set of bits sent in the second pilot, where the second set maycomprise the first set. Detection for a third pilot may be performedbased on the first and second detected values to obtain a third detectedvalue for all bits of information. For a non-hierarchical pilotstructure, detection may be performed independently for each pilot toobtain a detected value for the set of bits sent in that pilot.

For each pilot, a detection metric may be determined for each of aplurality of hypothesized values for that pilot. The hypothesized valueassociated with a largest detection metric may be provided as a detectedvalue for the set of bits sent in the pilot. Each hypothesized value forthe pilot being detected may comprise (i) a first part for the detectedvalues for pilots previously detected, if any, and (ii) a second partfor an unknown value for additional bits sent in the pilot beingdetected.

In one design, a noise estimate may be derived based on captured samplesfor the pilot being detected. A plurality of PN sequences may begenerated for a plurality of hypothesized values for the pilot. Thecaptured samples may be descrambled based on the plurality of PNsequences (e.g., in the time domain or the frequency domain) to obtain aplurality of sequences of descrambled samples. For frequency-domaindescrambling, the captured samples may be transformed to the frequencydomain to obtain received symbols. Modulation in the received symbolsmay be removed based on the PN sequence for each hypothesized value toobtain descrambled symbols for that hypothesized value. The descrambledsymbols for each hypothesized value may be transformed back to the timedomain to obtain a sequence of descrambled samples for that hypothesizedvalue. A plurality of detection metrics may be derived for the pluralityof hypothesized values based on the plurality of sequences ofdescrambled samples and the noise estimate. For example, the energy ofeach descrambled sample may be computed. The detection metric for eachhypothesized value may then be computed based on the energies for thesequence of descrambled samples and the noise estimate, e.g., as shownin equation (5).

FIG. 11 shows a design of an apparatus 1100 for receiving TDM pilots.Apparatus 1100 includes means for receiving a plurality of pilots in aplurality of time intervals, with the plurality of pilots carryingdifferent sets of bits for information sent in the pilots, and with eachset including some or all bits of the information (module 1112), andmeans for performing detection to recover a set of bits sent in each ofthe plurality of pilots (module 1114).

Modules 912 and 914 in FIG. 9 and modules 1112 and 1114 in FIG. 11 maycomprise processors, electronics devices, hardware devices, electronicscomponents, logical circuits, memories, etc., or any combinationthereof.

The techniques described herein may be implemented by various means. Forexample, the techniques may be implemented in hardware, firmware,software, or a combination thereof. For a hardware implementation, theprocessing units at a given entity (e.g., a base station or a terminal)a may be implemented within one or more application specific integratedcircuits (ASICs), digital signal processors (DSPs), digital signalprocessing devices (DSPDs), programmable logic devices (PLDs), fieldprogrammable gate arrays (FPGAs), processors, controllers,micro-controllers, microprocessors, electronic devices, other electronicunits designed to perform the functions described herein, a computer, ora combination thereof.

For a firmware and/or software implementation, the techniques may beimplemented with modules (e.g., procedures, functions, etc.) thatperform the functions described herein. The firmware and/or softwareinstructions may be stored in a memory (e.g., memory 532 or 582 in FIG.5) and executed by a processor (e.g., processor 530 or 580). The memorymay be implemented within the processor or external to the processor.The firmware and/or software instructions may also be stored in otherprocessor-readable medium such as random access memory (RAM), read-onlymemory (ROM), non-volatile random access memory (NVRAM), programmableread-only memory (PROM), electrically erasable PROM (EEPROM), FLASHmemory, compact disc (CD), magnetic or optical data storage device, etc.

The previous description of the disclosure is provided to enable anyperson skilled in the art to make or use the disclosure. Variousmodifications to the disclosure will be readily apparent to thoseskilled in the art, and the generic principles defined herein may beapplied to other variations without departing from the spirit or scopeof the disclosure. Thus, the disclosure is not intended to be limited tothe examples and designs described herein but is to be accorded thewidest scope consistent with the principles and novel features disclosedherein.

1. An apparatus comprising: at least one processor configured togenerate a plurality of pilots based on different sets of bits forinformation being sent in the plurality of pilots, each set includingsome or all bits of the information being sent, and to send theplurality of pilots in a plurality of time intervals; and a memorycoupled to the at least one processor.
 2. The apparatus of claim 1,wherein the plurality of pilots are sent in sequential order and carryoverlapping sets of bits for the information, with the set of bits foreach pilot comprising bits for pilots sent earlier, if any, and at leastone additional bit not yet sent.
 3. The apparatus of claim 1, whereinthe plurality of pilots carry non-overlapping sets of bits for theinformation.
 4. The apparatus of claim 1, wherein the at least oneprocessor is configured to generate a first pilot based on some of thebits for the information, to generate a second pilot based on all of thebits for the information, and to send the first and second pilots infirst and second time intervals, respectively.
 5. The apparatus of claim1, wherein the at least one processor is configured to generate a firstpilot based on a first set of bits for the information, to generate asecond pilot based on a second set of bits for the information, thesecond set comprising the first set, to generate a third pilot based onall of the bits for the information, and to send the first, second, andthird pilots in first, second, and third time intervals, respectively.6. The apparatus of claim 5, wherein the information comprises 12 bits,the first set comprises 2 bits, and the second set comprises 8 bits andincludes the 2 bits in the first set.
 7. The apparatus of claim 1,wherein the at least one processor is configured to generate apseudo-random number (PN) sequence for each pilot based on the set ofbits being sent in the pilot, and to generate each pilot based on the PNsequence for the pilot.
 8. The apparatus of claim 1, wherein for each ofthe plurality of pilots, the at least one processor is configured togenerate a pseudo-random number (PN) sequence based on the set of bitsbeing sent in the pilot, to generate pilot symbols based on the PNsequence, to map the pilot symbols to subcarriers used for the pilot,and to transform the mapped pilot symbols to obtain a sequence ofsamples for the pilot.
 9. The apparatus of claim 1, wherein a pilot sentfirst in time among the plurality of pilots comprises multiple copies ofa waveform.
 10. The apparatus of claim 1, wherein each of the pluralityof pilots is a time division multiplexed (TDM) pilot sent in arespective one of the plurality of time intervals.
 11. The apparatus ofclaim 1, wherein the information being sent in the plurality of pilotscomprises sector-specific information, or system information, or both.12. A method comprising: generating a plurality of pilots based ondifferent sets of bits for information being sent in the plurality ofpilots, each set including some or all bits of the information beingsent; and sending the plurality of pilots in a plurality of timeintervals.
 13. The method of claim 12, wherein the generating theplurality of pilots comprises generating a first pilot based on some ofthe bits for the information, and generating a second pilot based on allof the bits for the information.
 14. The method of claim 12, wherein thegenerating the plurality of pilots comprises generating a first pilotbased on a first set of bits for the information, generating a secondpilot based on a second set of bits for the information, the second setcomprising the first set, and generating a third pilot based on all ofthe bits for the information.
 15. The method of claim 12, wherein thegenerating the plurality of pilots comprises generating a pseudo-randomnumber (PN) sequence for each pilot based on the set of bits being sentin the pilot, and generating each pilot based on the PN sequence for thepilot.
 16. An apparatus comprising: means for generating a plurality ofpilots based on different sets of bits for information being sent in theplurality of pilots, each set including some or all bits of theinformation being sent; and means for sending the plurality of pilots ina plurality of time intervals.
 17. The apparatus of claim 16, whereinthe means for generating the plurality of pilots comprises means forgenerating a first pilot based on some of the bits for the information,and means for generating a second pilot based on all of the bits for theinformation.
 18. The apparatus of claim 16, wherein the means forgenerating the plurality of pilots comprises means for generating afirst pilot based on a first set of bits for the information, means forgenerating a second pilot based on a second set of bits for theinformation, the second set comprising the first set, and means forgenerating a third pilot based on all of the bits for the information.19. The apparatus of claim 16, wherein the means for generating theplurality of pilots comprises means for generating a pseudo-randomnumber (PN) sequence for each pilot based on the set of bits being sentin the pilot, and means for generating each pilot based on the PNsequence for the pilot.
 20. A processor-readable medium includinginstructions stored thereon, comprising: a first instruction set forgenerating a plurality of pilots based on different sets of bits forinformation being sent in the plurality of pilots, each set includingsome or all bits of the information being sent; and a second instructionset for sending the plurality of pilots in a plurality of timeintervals.
 21. The processor-readable medium of claim 20, wherein thefirst instruction set comprises a third instruction set for generating afirst pilot based on some of the bits for the information, and a fourthinstruction set for generating a second pilot based on all of the bitsfor the information.
 22. The processor-readable medium of claim 20,wherein the first instruction set comprises a third instruction set forgenerating a first pilot based on a first set of bits for theinformation, a fourth instruction set for generating a second pilotbased on a second set of bits for the information, the second setcomprising the first set, and a fifth instruction set for generating athird pilot based on all of the bits for the information.
 23. Anapparatus comprising: at least one processor configured to receive aplurality of pilots in a plurality of time intervals, the plurality ofpilots carrying different sets of bits for information sent in thepilots, each set including some or all bits of the information, and toperform detection to recover a set of bits sent in each of the pluralityof pilots; and a memory coupled to the at least one processor.
 24. Theapparatus of claim 23, wherein the at least one processor is configuredto perform detection for a first pilot to obtain a first detected valuefor a first set of bits sent in the first pilot, and to performdetection for a second pilot based on the first detected value to obtaina second detected value for all bits of the information.
 25. Theapparatus of claim 23, wherein the at least one processor is configuredto perform detection for a first pilot to obtain a first detected valuefor a first set of bits sent in the first pilot, to perform detectionfor a second pilot based on the first detected value to obtain a seconddetected value for a second set of bits sent in the second pilot, thesecond set comprising the first set, and to perform detection for athird pilot based on the first and second detected values to obtain athird detected value for all bits of the information.
 26. The apparatusof claim 23, wherein the at least one processor is configured to performdetection for each of the plurality of pilots based on detected valuesfor pilots previously detected, if any, to obtain a detected value forthe set of bits sent in the pilot being detected.
 27. The apparatus ofclaim 23, wherein for each of the plurality of pilots, the at least oneprocessor is configured to determine a detection metric for each of aplurality of hypothesized values for the pilot, and to provide ahypothesized value associated with a largest detection metric as adetected value for the set of bits sent in the pilot.
 28. The apparatusof claim 27, wherein each hypothesized value for the pilot beingdetected comprises a first part for detected values for pilotspreviously detected, if any, and a second part for an unknown value forat least one additional bit sent in the pilot being detected.
 29. Theapparatus of claim 23, wherein for each of the plurality of pilots, theat least one processor is configured to derive a noise estimate based oncaptured samples for the pilot, to generate a plurality of pseudo-randomnumber (PN) sequences for a plurality of hypothesized values for thepilot, to descramble the captured samples based on the plurality of PNsequences to obtain a plurality of sequences of descrambled samples forthe plurality of hypothesized values, to derive a plurality of detectionmetrics for the plurality of hypothesized values based on the pluralityof sequences of descrambled samples and the noise estimate, and toprovide a hypothesized value associated with a largest detection metricas a detected value for the set of bits sent in the pilot.
 30. Theapparatus of claim 29, wherein for each of the plurality of pilots, theat least one processor is configured to transform the captured samplesto frequency domain to obtain received symbols, to remove modulation inthe received symbols based on the PN sequence for each hypothesizedvalue to obtain descrambled symbols for the hypothesized value, and totransform the descrambled symbols for each hypothesized value to obtaina sequence of descrambled samples for the hypothesized value.
 31. Theapparatus of claim 29, wherein to derive a detection metric for ahypothesized value, the at least one processor is configured to computeenergy of each descrambled sample in a sequence of descrambled samplesfor the hypothesized value, and to compute the detection metric based onenergies for the sequence of descrambled samples and the noise estimate.32. A method comprising: receiving a plurality of pilots in a pluralityof time intervals, the plurality of pilots carrying different sets ofbits for information sent in the pilots, each set including some or allbits of the information; and performing detection to recover a set ofbits sent in each of the plurality of pilots.
 33. The method of claim32, wherein the performing detection comprises performing detection fora first pilot to obtain a first detected value for a first set of bitssent in the first pilot, and performing detection for a second pilotbased on the first detected value to obtain a second detected value forall bits of the information.
 34. The method of claim 32, wherein theperforming detection comprises performing detection for a first pilot toobtain a first detected value for a first set of bits sent in the firstpilot, performing detection for a second pilot based on the firstdetected value to obtain a second detected value for a second set ofbits sent in the second pilot, the second set comprising the first set,and performing detection for a third pilot based on the first and seconddetected values to obtain a third detected value for all bits of theinformation.
 35. The method of claim 32, wherein the performingdetection comprises, for each of the plurality of pilots, determining adetection metric for each of a plurality of hypothesized values for thepilot, and providing a hypothesized value associated with a largestdetection metric as a detected value for the set of bits sent in thepilot.
 36. An apparatus comprising: means for receiving a plurality ofpilots in a plurality of time intervals, the plurality of pilotscarrying different sets of bits for information sent in the pilots, eachset including some or all bits of the information; and means forperforming detection to recover a set of bits sent in each of theplurality of pilots.
 37. The apparatus of claim 36, wherein the meansfor performing detection comprises means for performing detection for afirst pilot to obtain a first detected value for a first set of bitssent in the first pilot, and means for performing detection for a secondpilot based on the first detected value to obtain a second detectedvalue for all bits of the information.
 38. The apparatus of claim 36,wherein the means for performing detection comprises means forperforming detection for a first pilot to obtain a first detected valuefor a first set of bits sent in the first pilot, means for performingdetection for a second pilot based on the first detected value to obtaina second detected value for a second set of bits sent in the secondpilot, the second set comprising the first set, and means for performingdetection for a third pilot based on the first and second detectedvalues to obtain a third detected value for all bits of the information.39. The apparatus of claim 36, wherein the means for performingdetection comprises, for each of the plurality of pilots, means fordetermining a detection metric for each of a plurality of hypothesizedvalues for the pilot, and means for providing a hypothesized valueassociated with a largest detection metric as a detected value for theset of bits sent in the pilot.
 40. A processor-readable medium includinginstructions stored thereon, comprising: first instructions forreceiving a plurality of pilots in a plurality of time intervals, theplurality of pilots carrying different sets of bits for information sentin the pilots, each set including some or all bits of the information;and second instructions set for performing detection to recover a set ofbits sent in each of the plurality of pilots.